Field of the Invention
The present invention relates to optically clear biofouling resistant coating organosiloxane compositions specially formulated for very high light transmission, and more particularly to coating compositions which can be applied to marine instruments and sensors. The compositions provide a biofouling resistant coating on the surface of the marine instruments and sensors which prevents underwater organisms from adhering and growing on the surfaces of the structures over a long period of time.
Description of the Prior Art
A large number of organisms such as barnacles, bacterial slimes, ascidians, serupulas, fresh- and salt-water mussels, polyzoan, green algae, sea lettuce and the like live in the waters of the sea, rivers, lakes and swamps. These plants and animals cause various types of damages, and particularly adhere to and degrade the performance of marine instruments and sensors.
The biofouling of marine and other aquatic instrumentation is a long-felt and well-established problem by those in industry, science and resource management, as biofouling inhibits the performance of marine instrumentation, thereby adversely affecting the data acquired as well as adding to the cost of maintaining the instruments. Problems due to biofouling of marine instrumentation have been occurring for many decades and continue to be a major factor inhibiting the effective use of submerged instruments.
Biofouling on the marine instrument housing causes messy handling of the instrument upon retrieval; increases the surface area of the housing thereby making the instrument more susceptible to forces imparted on it from current, waves or other moving water; increases the weight of the instrument both in and out of the water; increases personnel time to clean with an associated increase in operation and maintenance cost the biofouling that attaches to the surface area of the housing has a tendency to migrate towards the sensor area.
Additionally, the biofouling on the sensor elements can attenuate sensor signals, disrupt critical spacing between conductor elements, disable optical devices due to blockage of light transmission through their elements; block open ports of pressure or sensing chambers, clogs open flow cylinders of some sensors and some biofouling organisms such as barnacles can bore into the transducer elements, thereby damaging them.
Biofouling of marine instruments comprising a housing and sensor element continues to be a persistent problem. Prior attempts to address the problems associated with biofouling of sensor elements have involved using, mechanical wipers to remove biological material from the sensor elements; various grease types which work through ablative processes or through the incorporation of active agents such as pepper extracts or other traditional metal biocides, tributyl tin tablets that sterilize the local sensing area or chamber contained sensor area, using traditional paints containing active biocides, sensor encapsulation boxes that prevent light from contacting the sensor element when it is not in use and thereby prevent or limit biofouling, chlorine systems that often use electrolysis to generate chlorines from seawater, various chemical treatments that are injected into a closed chamber system and using copper mounting plates for sensor components.
Other prior attempts to address the problems associated with biofouling of housing elements include the use of various grease types which work through ablative processes or through the incorporation of active agents such as pepper extracts or other traditional metal biocides, use of traditional paints containing active biocides, or various types of tapes that are wrapped on the housings and then removed when the instrument is retrieved, thus removing the biofouling.
Prior art techniques have obvious limitations. For instance, use of grease for preventing biofouling of instrument housing may be initially effective; its effectiveness diminishes over time as the greases need to be periodically reapplied as the grease is washed off. Furthermore, greases may have adverse environmental effects as they are in some cases toxic to non-biofouling marine life and to workers handling and maintaining the marine instruments. On the other hand, paints or any opaque coating will not work on optical sensors as they will disrupt light transmission in the same manner that biofouling itself does. Additionally, metal biocide released from various paints or greases cannot work with electrode or electromagnetic sensor elements as they will disrupt the generated signal. Mechanical wipers have proven to improve the duration that optical instruments can be deployed. Fouling does however occur and the mechanical systems use a significant amount of battery power for those devices that are battery powered. Furthermore, paints containing active biocides or other biocide applications lose their efficacy over time. The copper mounting plates noted have moderate effectiveness in reducing biofouling accumulation. The use of tapes on instrument housing does not reduce the degree of biofouling but simply protects the instrument housing and allows the user to clean the instrument by removing the tape rather than scraping the instrument.
Where marine instruments have been coated with opaque biofouling resistant material, the coating occludes the identity of the instrument causing manufacturers to loose their identifying look and branding; serial numbers and other identification markings.
In order to solve the above problems, various coating compositions have previously been proposed. For example, U.S. Pat. Nos. 4,025,693 and 5,218,059, 5,958,116 disclose coating compositions which are prepared using a silicone rubber alone or as a mixture with silicone oil. US 20080166493 disclose silicone based coating compositions containing ceramic nanoparticles. US 20080255304 relate to integrally molded body of silicone resin and silicone rubber but does not teach an antibiofouling composition. Prior art does not provide optically clear silicones nor address the issue of poor silicone adhesion to a wide variety of marine instrument surfaces, particularly adhesion promotion in a manner that does not interfere with light transmission. Hence, there is need for biofouling resistant coating compositions specially formulated for very high light transmission without impeding the effectiveness of the submerged instruments.